Apparatus for edge grinding small objects



H F. FRUTH 23%,33

APPARATUS FOR EDGE GRINDING SMALL OBJECTS Filed July 28, 1943 2 Sheets-Sheet 1 Oct. 16, 1945.

INVENTO:

HQLFH Y 03 d. 16, 1945. H. F. FRUTH APPARATUS FOR'EDGE GRINDING SMALL OBJECTS Filed July 28, 1943' 2 Sheets-Sheet 2 INVENTOR. Hal FEW Paiented Oct. 16, 1945 APPARATUS FOR EDGE GRINDING SMALL OBJECTS Hal F. Fruth, Chicago, Ill., assignor to Galvin Manufacturing Corporation, Chicago, 111., a corporation of Illinois Application July 28, 1943, Serial No. 496,382

9 Claims.

The present invention relates to apparatus for grinding-the edges of small objects and more particularly to improved apparatus for finish grinding the edges of piezoelectric crystals in order to remove irregularities therefrom and to produce polished edgev surfaces thereon.

In the manufacture of certain parts or articles 7 which have relatively sharp edges formed at the sions required to produce the desired frequency characteristics, and are edge ground to remove irregularities from the edges thereof. The usual crystal blank is cut in the form of a fiat piece and is then reduced to rectangular dimensions slightly larger than the desired dimensions by grinding the sides and ends thereof on a suitable grinding wheel. According to conventional practice, all finish grinding operations are performed by hand, the edges and faces of the crystal being finish ground by bringing the desired surface to bear against an abrasive surface and manually moving the bearing surface of the crystal across the abrasive surface. These operations are tediously slow and require skilled labor in the performance thereof. They also result in considerable crystal breakage, particularly in the grinding of high frequency crystals having a thickness of seven mils or less. Moreover, the finished crystals obtained by using such grinding methods are not entirely satisfactory in opera tion. More specifically, the operating difficulties which have been experienced are attributable in large measure to the fact that it is apparently impossible with conventional edge grinding methods to obtain crystals which are free of edge irregularities. Such edge irregularities as' may be present in a finished crystal tend to produce spurious vibrating frequencies which are difiicult to stop when once started. Furthermore, the minute points which remain at the edges of the crystal have a tendency to break away, causing v crystal dust which remains on the surfaces of the crystals. These dust particles will sometimes change the frequency of vibration of the crystal or cause the vibration of the crystal to be entirely arrested.

It is an object of the present invention, therefore, to provide improved and exceedingly simple apparatus for grinding the edges of small objects or articles to remove discontinuities therefrom;

It is another object of the invention to .provide improved apparatus for edge grinding piezoelectric crystals in an improved-manner such that the disadvantages of the manual grinding meth ods now commonly in use are obviated, and an improved crystal structure having more stable operating characteristics is obtained.

According to another object of the invention, a controlled method of edge grinding small flat fibjects is provided in which the objects are produced to conform with precision accuracy to predetermined dimensional standards on a variable time basis with a minimum expenditure of man= ual labor.

It is a still further object of the invention to provide improved apparatus for grinding the edges of small objects or articles to produce edge bevels thereon, which apparatus is adjustable to vary the angles at which the bevels are cut.

It is still another object of the invention to provide grinding apparatus of the character described wherein an abrasively coated flexible belt is utilized to produce the desired abrading action.

According to a still further object of. the invention, facilities are provided for continuously oscillating the belt as it is driven, whereby the objects being abraded are slid back and forth across the abrasive surface as the abrasive surface is driven beneath the objects supported thereon.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be under,- stood by reference to the following specification taken in connection with the accompanying drawings, in which:

Fig. 1 is a front view illustrating improved grinding apparatus characterized by the features of the present invention;

Fig. 2 is a side view partially in sectionpof the apparatus shown in Fig. 1; and

Fig. 3 is a view partially in section of the ap iiparatus shown in Fi edge grinding apparatus there illustrated com.-

prises an endless flexible belt l0 which is provided at its inner side'with an abrasive surface I I. This belt may be formed of sandpaper, em-

ery cloth or the like having abrasive grit thereonof suitable hardness and fineness fo performa fineness of from No. 100 to No. 400 screen mesh depending upon the grinding speed desired. It will be understood that asuita'ble binder is utilized for cementing the particles of grinding material to the inner surface of the belt Ill. The belt is of substantial width and is supported to hang from a driving roller I2 so that the side portions thereof extend between the opposed surfaces of three additional driving rollers l3, l5 and IS. The four enumerated rollers have the same diameters and are respectively carried on shafts Ha, 13a, Ma and IE1: which are suitably journaled in the side members 8a and 8b of a rec-j tangular frame 8. They are arranged to be driven in synchronism by an electric motor I! rigidly mounted upon the .upper transverse member 8c of the frame 8. This motor is connected in driving relationship with the shaft 12a by means of the chain 18 which encircles the sprockets I'la and 12b respectively mounted upon the motor drive shaft and the roller supporting shaft In. The shaft 12a is'in turn. connected to drive the shaft [4a through a chain 19 which encircles sprockets l2c and Ma respectively mounted for rotation with the shafts 12a and. Ma. Meshing gears l3b, Nb and b, respectively mounted'for rotation with the shafts (3a, Ma and 15a are utilized to drive the rollers 13 and 14 from the shaft Ma. The gear Hb has a one to one drive ratio with each of the two meshing gears 13b and I51), and the two sprockets I20 and He also have a one to one drive ratio, so that all four of the rollers are driven at the samespeed. Thus, the rollers are driven in the directions indicated by the arrows respectively associated therewith, and are actuated at speeds such that the belt is extruded from between the rollers 13 and H at a uniform speed which exactly equals the speed at which the belt is drawn between the oppositely disposed rollers 14 and 05. With this arrangement, the portion of the belt which hangs freely from the underside of, the three horizontally aligned rollers l3, l4 and I5 forms a loop. the lowermost part of which is of curved trough-like configuration. The radius of curvature of this trough is of course dependent upon the diameter of the rollers and the extent to which the lower portion of the belt l0" hangs below the three horizontally aligned rollers I3, I 4 and I5. By suitably proportioning these'factors, any desired radius of curvature of the trough may be obtained.

The curved side walls of the trough formed at the lower end of the belt ID are utilized to support at the edges thereof the objects or articles 9 which are to be ground, so that when the belt is continuously rotated in one direction or is oscillated back and forth between two extreme positions, the edge portions of the articles are subjected to an abrading Or grinding actiorrr" For the. purpose of retaining the articles within the trough-like portion of the belt, an enclosing housing 2| is provided which is supported within the lower portion of the frame 8 by means of screws 20 and includes at either end thereof retaining walls 22 and 23. As best shown in Fig. 3 of the drawings, these retaining walls are disposed closely adjacent opposite edges of the belt 10 and, in combination. close the trough-like por- 9 disposed therewithin from sliding out of the trough at the ends thereof. In order continuously to change the positions of the objects with respect to the belt, thereby to bring different edge portions of each object to bear against the abrasive surface of the belt, suitable bafiie strips are provided which are adhesively secured to the I inner belt surface. To secure adequate adhesion thereof. is disposed downwardly.

of the baffle strips to the inner surface of the belt, the abrasive may be scraped from the portions of the belt surface to which the strips are to be cemented. More specifically, anhuninterrupted strip 24,-which extends transversely of the belt, and may consist of a strip of adhesive tape applied to the inner surface of the belt, is

provided for tumbling the objects Or articles end for end so that first one and then the other face Additional bafile strips or spots 25 which are spaced apart transversely of the belt at a different point along the length thereof and likewise consist of short strips of adhesive tape, may be provided for the specific purpose of rotating the articles edge for edge through ninety degrees without tumbling the same in order successively to bring different pairs of the edge surfaces to bear against the abrasively coated inner surface of the belt. These laterally spaced-apart bafile strips orspots are preferably of circular pattern.

For the purpose of continuously oscillating or tilting the belt Ill, thereby to slide the objects back and forth between the ends of the troughlike portion thereof, the frame 8 is pivotally mounted at its upper end upon a pivot rod 1, and a slow speed motor 6 is provided for rocking the lower end of the frame so that the frame and the parts carried thereby are oscillated pendulum fashion about the pivot pin I. The motor 6 and the rod 1 are rigidly mounted upon the supporting structure for the apparatus, and the motor shaft is crank arm connected to the lower end portion of the frame member 8a by means of a disk Ba and an arm 5. More specifically, the arm 5 is provided with one end which is pivotally connected by axis means 4 to the frame member 8a and with an opposite end which is pivotally connected by axis means 3 to a radially oifset portion of the disk 6a. Preferably the speed of operation of the motor 6 is so related to the width of the belt I that an object or crystal 9 supported within the belt trough will slide from one end of the trough to the other and then back to its starting point during each revolution of the motor. In order to counterbalance the combined weight of the movable parts projecting outwardly from the frame side member 817. thereby to minimize fluctuations in the load imposed upon the slow speed oscillating motor 8, the belt driving motor I! is mounted upon the upper frame member 80 so that its center of gravity is disposed to the left of the vertical plane which bisects the frame, as viewed in Fig. 1 of the drawings.

In utilizing the above-described apparatus to grind the edges of small thin objects of rectangular shape, such, for example, as the illustrated piezoelectric quartz crystals 9, the crystals are preferably disposed within the trough formed at the lower end of the belt in so that the oppositely disposed lower edges thereof bear against the abrasively coated sides of the trough. The capacity of the apparatus is of course only limited by the width of the belt and the dimensions of the crystals to be ground, but it is noted that in tion of the belt to prevent the articles or parts order to prevent stacking of the crystals the available trough area shouldnot be overloaded with too large a number of crystals. After the trough portion of the belt has been loaded, operation of the motor I! to drive the rollers l2, l3, I4 and I5 is initiated, and operation of the motor 6 to oscillate the lower end of the assembly about the pivot rod 1 is started. With the enumerated rollers rotating in the directions respectively indicated by the arrows associated therewith, the belt is driven in a closed orbit continuously in the same direction and with substantially no distortion of the configuration of that portion thereof which defines the trough across which the objects are bridged. During movement of the belt Hi, the abrasively coated inner surface thereof is moved across the bearing edge surfaces of the crystals to abrade these edges. This abrading action is supplemented by that Which is produced by sliding the'crystals back and forth along the length of the trough-like portion of the belt, this sliding action being produced at a slow speed through the action of the motor 6 to tilt the belt so that the trough-like portion thereof is alternately reversely inclined to the horizontal. Thus, the sliding of the crystals back and forth between the ends of the belt trough prevents scratches from being formed transversely of the crystal edges and accentuated, due to the abrasion of the edges with the same longitudinal segment of the belt surface. Similarly, the sliding of the abrasive surface beneath the edges of the crystals under the influence of the four drivingv rollers, prevents scratches from being formed longitudinally of the crystal edges and accentuated as the crystals are slid back and forth between the ends of the belt trough. As the abrading action proceeds, rounded chamfers or bevels are produced at the edges of the crystals. In this regard it is noted that the contact pressure existing between the edge surfaces of each crystal and the abrasive surface is determined substantially entirely by the weight of the crystal. This pressure is of a relatively low order of magnitude, such that scratching of thecrystal edgesurfaces is further minimized. The weight of each crystal is, however, suflicient to prevent the crystal from being carried any substantial distance up the leading wall of the belt due to the movement of the belt beneath the bearing surfaces thereof.

Each time the baille strip 24 is moved to engage the left end or side surface of one of the crystals, as viewed in Fig. 2 of the drawings, the

engaged crystal is carried upwardly during con-' tinued movement of the belt until it reaches a position such that it will topple over backward, whereby the opposite fiat surface of the crystal faces downward and a different pair of edges of the crystal is brought into engagement with the abrasive-surface. Each time one of the baille strips or spots 25'is moved to engage a corner portion of one of the crystals and during continued movement of the belt, the weight of the engaged crystal causes the crystal to spin about away from the engaging baflle spot whereby the crystal is moved through an angle of ninety degrees with respect to the beltwithout toppling over. Thus, those edges which are disposed substantially at ninety degrees with respect to each other on a rectangular object are successively utilized to support the object upon the abrasively I coated inner surface of the belt, whereby each pair of edges is suitably abraded during the continuous movement of the belt. As each crystal is spun about by one of the baflle spots 25, the corner edges thereof are also abraded by the abrasive surface ll. edges of each crystal also become rounded or chamfered after the grinding operation has continued for a reasonable time interval.

It will be apparent from the above explanation that due to the action of the baffle elements 24 and 25, the crystals or other objects are continuously moved at random to change the positions thereof relative to the belt o that all edge surfaces thereof are subjected to the abrading action. The speed at which the edge chamfers or bevels are formed upon the objects is determined by the fineness of the abrasive material employed. It is also dependent upon the speed at which the belt I0 is operated. By suitably proportioning these two factors on an experimental basis and in their relationship to the hardness of the articles or objects being ground, the apparatus may easily be calibrated to produce a chamfer or bevel of given and uniform depth or width when the apparatus is operated for a measured time interval. In this regard it should be noted that due to the action of the baflle elements 24 and 25, all edge portions ofthe articles are subjected to approximately the same amount of abrading action durin a given time interval, so that the bevels or chamfers which are produced during the interval are of uniform depth or width.

The degree of chamfering or, stated in other words, the angle of the chamfer which is produced through operation of the apparatus in the manner explained above, is of course dependent upon the radius of curvature of the trough-like belt portion in its relationship tothe flat dimensions of the objects being ground. Preferably, the radius of curvature of the trough formed by the lower end of the belt is such that in the grinding of small rectangular objects, one object may be disposed widthwise transversely of the trough with a second object disposed lengthwise transversely of the trough directly thereabove without engagement between the adjacent surfaces of the two objects. As thus arranged, the weight of each object alone determines the contact pressure between the bearing edge surfaces thereof and the abrasive surface of the belt, with the result that uniform abrading is obtained.

If increased contact pressure is desired between the edge portion of a particular article or object and the abrasive surface of the belt I!) for the purpose of expediting the abrading operation, the article may be supported by means of a small suction cut at the end of a stick and manually held in a position such that the desired pair of oppositely disposed edges bear against the trough-like inner surface of the belt Ill. In such case, the motor 6 is not operated and the desired contact pressure is obtained by manually pressing the bearing edges of the object against the abrasively coated belt surface. When the desired grinding of one pair of edges is completed, the article may then be turned end for end or face for face in order to bring another pair of oppositely disposed edges into engagement with the abrasive surface of the belt.

From the above explanation it will be understood that in accordance with the present invention, exceedingly simple apparatus is provided which may be utilized with a minimum amount of manual labor to rapidly produce edge bevels or chamfers of any desired configuration at the edge portions of small objects. Although the apparatus is particularly suited for use in the edge grinding of piezoelectric crystals of rec- Accordingly, the cornertangular configuration, it will be understood that it may also be employed with equal facility in grinding to predetermined dimensions the edges of small objects of practically any pattern and material. For example, the apparatus is well adapted for use in the edge grinding of optical lenses of round, oval or other configurations. .It may also be used in the edge grindin of small flat metal parts of any desired pattern.

While different embodiments of the invention have been disclosed, it will be understood that various modifications may be made therein, which are within the true spirit and scope of the in.- vention.

I claim: 4

1. Apparatus for grinding the edges of a relatively small object, comprising a flexible belt, means supporting said belt so that a portion thereof provides a trough having sides for supporting the object at the edges thereof, said belt having an abrasive surface at the side thereof upon which the edges of the object are adapted to be supported, means for driving said belt so that said abrasive surface is continuously moved relative to the edges of said object, and means carried by said belt for contacting said object, therebycontinuously to change: at random the position of the object relative to said belt so that different edge portions thereof are brought to bear against said abrasive surface.

2. Apparatus for grinding the edges of a relatively small object. comprising an endless flexible belt having an abrasive surface at theinner side thereof, means supporting said belt so that a portion. thereof hangs free to provide a trough having curved sides for supporting the object at the edges thereof, and'means for driving said belt so that said abrasivesurface is continuously moved relative to the edges of the object supportedupon the curved sides of said trough.

' 3. Apparatus for grinding the edges of a relatively small object, comprising an endless flexible continuously and at random changing the position of said object relative to said belt so that different edge portions of the object are brought to bear against said abrasive surface.

6. Apparatus for grinding the edges'of relatively small thin rectangular objects, comprising an endless flexible belt having an abrasive inner surface, means supporting said belt so that a. portion thereof provides a trough of such dimensions that twoof said objects may be bridged between the sides of said trough one above the other-and with their faces separated when the two objects are respectively disposed widthwise and lengthwise of said trough in the order of their elevation in said trough, means for driving said belt continuously in one direction so that said abrasive surface is continuously moved relative to the edges of the objects bridged between and bearing against the sides of said trough, and baille means secured to the inner surface of said belt for continuouslychanging at random the positions of said objects relative to said belt so that different edge portions of the objects are brought to bear against said abrasive surface.

'7. Apparatus for grinding the edges of a relatively small object, comprising a flexible belt, means supporting said belt so that a portion thereof provides a trough having sides for bearing against the object at the edges thereof, said belt having an abrasive surface at the side thereof upon whichthe edges of .the object are adapted to bear, means for driving said belt so that said abrasive surface is continuously moved relative to the edges of said object, and means for oscillating said belt so that said object is slid back and forth over said surface between the endsof belt having an abrasive surfaceat the inner side thereof, means supporting said .belt so that a portion' thereof hangs free to provide a trough having curved sides "for supporting the object at the edges thereof, means for driving said belt that said abrasive surface is continuously moved relative to the edges of the object supported upon having curved sides for supporting the object at the edges thereof, means for driving said belt so that said abrasive surface is continuously moved relative to the edges of the object supported upon the curved sidesof said trough, retaining walls closing the endsof said trough to retain the object within said trough, and means carried by said belt for continuously changing at random the position 'of the object relative to the belt so that different edge portions of. the object are brought to bear against said abrasive sur face. I F

5. Apparatus for grinding the edges of a relatively small object, comprising an endless flexible belt having an abrasive surface at the inner side thereof, means supporting'said belt so that a portion thereof hangs free to provide a trough havsaid trough.

8. Apparatus for grinding the edges of a relatively small object, comprising a flexible belt,

- means supporting said belt so that a portion thereof provides a trough having sides for supporting the object'at the edges thereof, said belt having an abrasive surface at the side thereof upon which the edges of the object are adapted to be supported, means for driving said belt so that said abrasive surface is continuously moved relative to the edges of said object, means for oscillating said belt so that said object is slid back and forth over said surface between the ends of said trough, and means for continuously changing at random the. position of the object relative to said-belt so that different edge portions thereof are brought to bear against said abrasive surface.

9. Apparatus for grinding the edges of a relatively small object, comprising an endless flexible belt having an abrasive surface at the inner side thereof, means supporting said belt so that a portion thereof'hangs free to provide a trough having curved sides for supporting the object at the edges thereof, means, for driving said belt so that 

